In "Yes Man," Jim Carrey plays Carl, an antisocial Los Angeles bank-loan officer who agrees to stop saying "no" - to friends, strangers, co-workers, the homeless; to fun, life, Mormons, even the horny old lady (Fionnula Flanagan) in his apartment complex. He twists, shouts, does a round of Dance Dance Revolution, plans a bridal shower, attends what must be the last rave in California, learns Korean, goes to a Harry Potter costume party, and courts Zooey Deschanel.

Yet the joys of affirmation appear lost on Carrey, who never looks truly happy. It's entirely possible that I'm projecting my forced smiles onto Carrey's face. But he seems to hold this entire exercise (it is, alas, a workout) in contempt. Perhaps he thought he was through with these high-concept, one-note comedies, having failed to top the physical genius of "Liar Liar" in 1997, and having made a mild breakthrough of sincerity in 2003's "Bruce Almighty."

While Carrey was off exploring his dramatic range in movies as radically different as "Man on the Moon," "Eternal Sunshine of the Spotless Mind," and the execrable "The Number 23," the landscape for movie clowns changed. He does not belong to the fraternity that has come to dominate Hollywood comedy in this decade. Vince Vaughn, Ben Stiller, Will Ferrell, Owen Wilson, on one hand, and the writer-director-producer Judd Apatow, on the other, share a franchise on the genre. It's strange to say, but Carrey is an outsider in a rambunctious style he helped create. For "Yes Man," he turns in what feels like a Jim Carrey impersonation - 104 minutes of high-energy heartlessness.

The gist of it all is that Carl must carpe his diem. He attends a seminar led by a yes guru (Terence Stamp, comically smug) where everyone around Carl is happy (or something like it), so why shouldn't he be, too? In our pharmaceutical age, there's probably a great farce to be made about emotional conformity. This movie, directed by Peyton Reed and adapted from Danny Wallace's novel by three writers, feels made from quirky-comedy instant mix: just add heart. It's a cynical attempt, ultimately, to make obnoxious people palatable by throwing them into a tub of romantic comedy.

Casting Deschanel as The Girl is not the wonderful stroke it once was. Between this film and "The Happening," she seems more warmed over than Carrey. Deschanel glides through "Yes Man" with a cute haircut and cuter clothes, fronts a band called - quirk alert #1! - Munchausen By Proxy (they have a semi-funny song about booty calls), and - quirk alert #2 - teaches a jogging photography class. We've seen her scoot through this part before in "Elf" and "Failure to Launch." There are probably a dozen better ways for her to spend her time (although few as lucrative), so it seems too soon for her to be on autopilot. For one thing, where's her "Yes Woman"?

That, of course, is the biggest problem with this movie - not that it's mediocre, dull, or barely written (though it's guilty on all counts). It's that Carrey himself is miscast. This is a star-making part as opposed to a part for a star committing a repeat offense. I watched Carrey ride a Ducati motorcycle in a hospital gown during the climax of this movie and thought about how much more fun it would have been to see a fresher face (Michael Cera's, Robert Pattinson's, or Paul Dano's) do that and all of Carl's exclamatory slapstick, to see someone care enough to make a character out of this.

If Carrey looks resentful or bored, it may be because he's made things too easy for himself. He doesn't have to worry about breaking character in "Yes Man." He's not playing one.